NOTE: This item is not available outside the Texas A&M University network. Texas A&M affiliated users who are off campus can access the item through NetID and password authentication or by using TAMU VPN. Non-affiliated individuals should request a copy through their local library's interlibrary loan service.
Catalytic and mechanistic studies of some anionic transition metal carbonyl hydrides
Abstract
As PPN⁺ (bistriphenylphosphineimminium) salts the anionic metal hydrides HFeM(CO)₉⁻ (M = Cr, Mo, W) were shown to be olefin isomerization catalysts under mild conditions (25°C, fluorescent lighting) toward the conversion of allylbenzene to the cis- and trans-propenylbenzenes and 1-hexene to internal olefins. The use of DFeM(CO)₉⁻ as an olefin isomerization catalyst was found to lead to the incorporation of d-label into the olefinic products. The activity of HFe(CO)₄⁻ was examined in the presence of alkali metal ions (Li⁺ or Na⁺) as well as in the presence of hydride abstracting agents (Ph₃C⁺ or BF₃). Evidence presented suggests the role of M(CO)₅⁰ to be similar to the alkali cations in promoting CO labilization and thus promoting catalysis on the Fe-H⁻ center. The reaction of H₂ with species of the type BM(CO)₅⁻ (B = Bronsted base; M = Cr, Mo, W) was shown to lead to the formal products of heterolytic cleavage, HB and HM(CO)₅⁻. For B = OAc⁻ or HM(CO)₅⁻, the catalytic hydrogenation of aldehydes, ketones, and α,β-unsaturated ketones was carried out. Mechanistic models consistent with observations made using in situ high pressure FTIR and isotopic labelling studies include (1) ligand assisted heterolytic activation of H₂, and (2) an alkoxide stabilized oxidative addition (dihydride) product or a base stabilized η²-H₂-metal carbonyl intermediate. Subsequent steps involve hydride attack on the carbonyl carbon followed by protonation to produce the alcohol product. For M(CO)₅R⁻, with B formally equal to R⁻ (R = Me, Ph, Bzl), products of simple elimination (or R⁻/H⁻) exchange), RH and HM(CO)₅⁻, were observed for M = W with activities Me > Ph >> Bzl. For M = Cr, carbonyl insertion products, i.e., aldehydes and alcohols were observed. Comparison studies were performed on the anionic iron alkyls, RFe(CO)₄⁻ (R = Me, Bzl). Like the W alkyls, products were those of simple elimination, RH and HFe(CO)₄⁻. A mechanistic model consistent with observed results involves the intermediacy of a molecular H₂ complex for the group 6 complexes. For the iron alkyls, the oxidative addition product RFe(H)₂(CO)₃⁻ is assumed to be an intermediate. For the heterobimetallic system RFeW(CO)₉⁻, with B = RFe(CO)₄⁻ (R = H, Me), products formed were HFe(CO)₄⁻, W(CO)₆, μ-HW₂(CO)₁₀⁻, and HFe₃(CO)₁₁⁻. Mechanisms proposed include (1) CO labilization of the heterobimetallic system followed by oxidative addition of H₂ on the Fe center, and (2) heterolytic activation of dihydrogen between the metal centers.
Description
Typescript (photocopy).Collections
Citation
Tooley, Patricia Ann (1986). Catalytic and mechanistic studies of some anionic transition metal carbonyl hydrides. Texas A&M University. Texas A&M University. Libraries. Available electronically from https : / /hdl .handle .net /1969 .1 /DISSERTATIONS -17162.
Request Open Access
This item and its contents are restricted. If this is your thesis or dissertation, you can make it open-access. This will allow all visitors to view the contents of the thesis.